Green Chemistry Based Synthesis of Zinc Oxide Nanoparticles Using Plant Derivatives of Calotropis gigantea (Giant Milkweed) and Its Biological Applications against Various Bacterial and Fungal Pathogens

Abstract

Nanotechnology is a burning field of scientific interest for researchers in current era. Diverse plant materials are considered as potential tool in green chemistry based technologies for the synthesis of metal nanoparticles (NPs) to cope with the hazardous effects of synthetic chemicals, leading to severe abiotic climate change issues in today's agriculture. This study aimed to determine the synthesis and characterization of metal-based nanoparticles using extracts of the selected <i>plant Calotropis gigantea</i> and to evaluate the enzyme-inhibition activities and antibacterial and antifungal activity of extracts of metal-based zinc nanoparticles using <i>C. gigantea</i> extracts. The crystal structure and surface morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). <i>C. gigantea</i> was examined for antimicrobial activity against clinical isolates of bacteria and fungi. The water, ethanolic, and acetone extracts of <i>C. gigantea</i> were studied for their antagonistic action against bacterial strains (<i>E. coli</i>, <i>S. aureus</i>, <i>P. multocida</i>, and <i>B. subtilis</i>) and selected fungal strains (<i>A. paracistic</i>, <i>F. solani</i>, <i>A. niger</i>, <i>S. ferrugenium,</i> and <i>R. nigricans</i>). In vitro antimicrobial activity was determined by the disc diffusion method, <i>where C. gigantea</i> wastested for <i>AChE</i> and <i>BChE</i> inhibitory activity using Ellman's methodology. The kinetic analysis was performed by the proverbial Berthelot reaction for urease inhibition. The results showed that out of all the extracts tested, ethanolic and water extracts possessed zinc nanoparticles. These extracts showed the maximum zone of inhibition against <i>F. solani</i> and <i>P. multocida</i> and the lowest against <i>S. ferrugenium</i> and <i>B. subtilis</i>. A potential source of <i>AChE</i> inhibitors is certainly provided by the abundance of plants in nature. Numerous phyto-constituents, such as <i>AChE</i> and <i>BChE</i> inhibitors, have been reported in this communication. Water extract was active and has the potential for in vitro <i>AChE</i> and <i>BChE</i> inhibitory activity. The urease inhibition with flower extracts of <i>C. gigantea</i> revealed zinc nanoparticles in water extracts that competitively inhibited urease enzymes. In the case of cholinesterase enzymes, it was inferred that the water extract and zinc nanoparticles have more potential for inhibition of <i>BChE</i> than <i>AChE</i> and urease inhibition. Furthermore, zinc nanoparticles with water extract are active inthe inhibition of the bacterial strains <i>E. coli</i>, <i>S. aureus</i>, and <i>P. multocida</i> and the fungal strains <i>A. paracistic</i>, <i>F. solani</i>, and <i>A. niger</i>.